A precision instrument consisting of a dial indicator mounted on a block which moves at right angles to the support frame known as the sled. The sled has two-line contact points which are at all times in alignment with the walls of the cylinder. The gage is equipped with a movable dial, and a handle is provided for insertion of the gage into a bore or cylinder. It is used to check and inspect the diameters of cylinders for taper, out of roundness, and accurately transfer the diameters of the cylinder bores.